Microcircuits used in microwave and millimeter-wave applications (“high-frequency microcircuits”) typically have a number of various devices and circuits (“electrical components”) combined in a common metal housing. Transmission structures between the electrical components are very important because they can affect the performance of the high-frequency microcircuit. It is generally desirable that these transmission structures have low loss in order to maximize the power transferred from one electrical component to another, and that parasitic impedance and capacitance is minimized in order to maintain constant electrical impedance. It is also generally desirable to minimize unwanted electrical coupling from one electrical component to another by maximizing the electrical isolation between electrical components. That is, it is desirable to avoid transmission paths between devices other than the intended interconnect path.
A wide variety of transmission lines are used in and between conventional high-frequency microcircuits, including parallel wire, twisted wire, coaxial, slab line, microstrip, coplanar waveguide and waveguide transmission lines. The electronic components of a high-frequency microcircuit are often arranged in a machined metal housing that provides environmental protection and electromagnetic shielding. The metal housing is also often machined to avoid electromagnetic radiation from one component to another; however, the use of simple interconnects, such as wire, ribbon, or mesh bonds, between electrical components in a high-frequency microcircuit often results in higher-order electromagnetic modes that affect isolation between components.
Coplanar waveguide (“CPW”) or microstrip interconnects are also used in high-frequency microcircuits; however, a portion of the electromagnetic field in such structures is concentrated in the dielectric material of the structure, which results in loss. Furthermore, CPW and microstrip interconnects are also susceptible of undesirable coupling of power through higher-order modes, thus reducing isolation between electronic components.
Thus, electrical interconnects for use in high-frequency microcircuits that provide low loss and high isolation are desirable.